When My Pet Became the Villain

The villain was reincarnated as an extra in a novel where she was destined to die early. After 18 years of living as a slave, mistreated by her family, she finally escapes just before her parents forcibly sell her to a villain. In a rural village, she spends a short but happy time with Momo, a dog she cares for. But three months later, the dog disappears. She is caught by her family and sold to the villain, expecting to be killed. However, just when she is about to die, the villain reveals himself—'Why are you so surprised? It's me, your puppy Momo.' (Source: Anime-Planet)